Flavor physics and CP violation

Abstract

We currently live in the age of the CKM paradigm. The 3 × 3 matrix that links (d, s, b) quarks to (u, c, t) in the charged current weak interaction, being complex and nominally with 18 parameters, can be accounted for by just 3 rotation angles and one CP violating (CPV) phase, with unitarity and the CKM phases triumphantly tested at the B factories. But the CKM picture is unsatisfactory and has too many parameters. The main aim of Flavor Physics and CP violation (FPCP) studies is the pursuit to uncover New Physics beyond the Standard Model (SM). Two highlights of LHC Run 1 period are the CPV phase φ s of B s mixing and B s → µ + µ − decay, which were found to be again consistent with SM, though the saga is yet unfinished. We also saw the emergence of the P 5 angular variable anomaly in B 0 → K * 0 µ + µ − decay and R K ( * ) anomaly in B → K ( * ) µ + µ − to B → K ( * ) e + e − rate ratios, and the BaBar anomaly in B → D ( * ) τ ν decays, which suggest possible New Physics in these flavor processes, pointing to extra Z , charged Higgs, or leptoquarks. Charmless hadronic, semileptonic, purely leptonic and radiative B decays continue to offer various further windows on New Physics. Away from B physics, the rare K → πνν decays and ε /ε in the kaon sector, µ → e transitions, muon g − 2 and electric dipole moments of the neutron and electron, τ → µγ, µµµ, eee, and a few charm physics probes, offer broadband frontier windows on New Physics. Lastly, flavor changing neutral transitions involving the top quark t and the 125 GeV Higgs boson h, such as t → ch and h → µτ , offer a new window into FPCP, while a new Z related or inspired by the P 5 anomaly, could show up in analogous top quark processes, perhaps even link with low energy phenomena such as muon g − 2 or rare kaon processes. In particular, we advocate the potential new SM, the two Higgs doublet model without discrete symmetries to control flavor violation, as SM2. As we are close to the alignment limit with h rather SM-like, flavor changing neutral Higgs couplings (FCNH) are suppressed by a small mixing angle, but the exotic Higgs doublet possesses FCNH couplings, which we are just starting to probe. As LHC Run 2 runs its course, and with Belle II B physics program to start soon, there is much to look forward to in the flavor and CPV sector. *

CP Violation for the Heavens and the Earth

“…We had pointed out earlier [47] that g2HDM could in principle make the ratio B(B → µν)/B(B → τν) deviate from the SM expectation of 0.0045, where 2HDM II shares the same value [45]. But it was only by checking explicitly [46] that we found that, indeed, B → τν would be SM-like, but B → µν could be more easily shifted, even when one respects Eq.…”

Scalar leptoquark effects on $$B \rightarrow \mu \bar{\nu }$$ decay

“…which is relatively precise (subject to mild QED corrections) since it involves only lepton masses. The prediction for 2HDM type II is the same [1,4,5]. The B → ν ( = μ, τ ) decay rates can deviate from SM predictions in the presence of the SLQ S 1 .…”

“…The B → μν decay is further helicity suppressed, and has not been observed so far. It was pointed out recently that, while the ratio B(B → μν)/B(B → τν) is predicted to be the same for both SM and the popular 2HDM type II [1], the value could deviate [4,5] from the SM expectation in the more general 2HDM (g2HDM) that allows extra Yukawa couplings.…”

Direct CP violation in beauty and charm hadron decays

“…Many good reviews exist addressing CP violation in hadrons (see, for example, [35][36][37][38][39]). This work is dedicated exclusively to discussing direct CP violation in b-and c-hadron systems.…”